JPH0432132B2 - - Google Patents

Abstract

Disclosed is a system for remelting light gauge scrap metals which includes a remelting furnace with separate heating and melting chambers and pump means for induc- . ing circulation of molten metal between the two. Also included are auger means adapted to include light gauge "floating" scrap metal from the melt into the central zone of the melt.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates generally to the field of remelting metal scrap, and more particularly to the field of remelting metal scrap, particularly lightweight aluminum scrap, such as sheet metal scrap, machining cuttings,
and relating to the field of remelting aluminum soft drink cans.

A major concern of the secondary metal industry is the regeneration of oxides and gases that are contained, trapped, or dissolved in the molten metal during the remelting of scrap metal. These oxides are of interest because the prior formation of oxides reduces the proportion of remelted scrap metal that can ultimately be sold as a final product. This scrap portion is referred to as "melt loss" which is no longer usable due to oxides formed during remelting.

Impurities are formed during remelting when highly reactive liquid metal surfaces come into contact with reactive gases such as oxygen or hydrogen. The primary source of hydrogen and oxygen is the combination of air and combustion gases used for combustion in the remelting furnace. In order to eliminate impurities in the remelting of scrap metal, appropriate measures are taken to minimize the surface area of the reactive scrap metal exposed to reactive gases and to eliminate the molten metal containing flux. Means are used to remove impurities by regeneration.

In the field of remelting scrap metal, the active measures used to prevent or inhibit the formation of oxides during remelting are generally as follows:
A fluid bath of molten metal is created in the furnace by first remelting high mass, low surface area (heavy gauge) material, and this bath is then converted into flux and dross. )
Once the molten metal pool has formed in the furnace, the molten metal is The scrap is then brought to a set level and allowed to flow at a rate proportional to the addition of further scrap. A shielding coating over the bath is formed by melting the surface of the bath.
Impurities assisted by the flux float to the surface and create a crust or "float" at the top of the bath. This scum exists in solid or plastic form.

Immediately beneath the dross is a semi-molten, semi-plastic metal "skim" containing varying degrees of impurities. Although this skim and float is usually removed continuously or intermittently from the furnace to prevent large build-up, some skim and float may be placed on the surface of the furnace to remove oxygen from the molten metal present below. It may be advantageous to act as a shielding agent to prevent further contact with other atmospheric gases. The skim and flotsam removed from the furnace are processed to fully solidify and either be discarded or the metals contained are recycled.

Melting scrap metal is an energy-intensive process, and additional energy is required to convert and maintain the scrap metal in a molten state. The form of energy used is electricity or heat generated by a combustion source. The introduction of scrap metal into a heat-generating zone generates a large amount of thermal energy when relatively cold scrap metal is introduced into the heat-generating zone and when this heat-generating zone is exposed to cold atmospheric air during the introduction of the scrap. The problem is that it is lost. Additionally, impurities are formed when the scrap comes into sufficient contact with fuel gases, combustion gases, and atmospheric air to melt. Therefore, as a general suggestion, metal melting furnaces are designed to specifically prevent heat losses when the heat generating zone is exposed to atmospheric air and to remove impurities from the reaction of fuel gases, combustion gases and atmospheric air with the molten scrap. Improvements have been made in an attempt to specifically prevent the formation of

One attempt to improve the furnace took the form of providing an additional chamber outside the hearth other than the refractory material, a "melting" chamber. A refractory "wall" separates the burner from the melting chamber. This wall is provided with an inlet/outlet for flowing molten metal between the melting chamber and the heating chamber. This port is located below the fluid level normally set in the molten metal. The scrap is introduced into the melting chamber where it comes into contact with molten metal. With such means, the scrap is always shielded from undesirable effects of the burner and the burner does not lose useful thermal energy to the atmosphere.

In attempts to use such isolated chambers for remelting furnaces, natural convection of the molten metal itself through the wall openings between the isolated chambers maintains the molten metal in a molten state within the melting chamber. It was determined that the solid state scrap metal was not suitable for transferring heat at a sufficient rate to melt the solid scrap metal that was being added. Attempts to utilize special refractory compositions designed to conduct heat from the heating chamber to the melting chamber have had limited success, with only relatively small amounts of scrap not reducing the melting temperature below an acceptable level. I was able to successfully add it. The addition of a special molten metal pump is ultimately necessary to ensure that the melter temperature is maintained high enough that solidification does not begin to occur.

Such pumps, which are commercially available, are usually made from graphite or other refractory materials that resist degradation. The addition of a molten metal circulation pump to the isolated chamber melting furnace system described above enables commercial application of the system to the melting and remelting of relatively heavy gauge scrap. However, low mass, high surface area (light gauge) metals are increasingly being used in commercial applications, and as a result, this light gauge scrap is increasing in quantity for recycle use.
In particular, the use of soft drink cans has increased significantly. Additional problems are encountered with the remelting of this light gauge scrap and new techniques are needed to reduce the amount of melt loss to an acceptable level.

Molten metals are characterized by very high surface tension. Generally speaking, in a metal remelting furnace, if heavy gauge scrap is dropped into the molten metal, gravity will cause it to sink rapidly into the molten fluid. However, due to surface tension and the fact that light gauge scrap tends to "float" above the surface over long periods of time due to scum and skim on the surface of the molten metal, immersing it in the fluid This is even more difficult. Much of the light gauge scrap used is lost to oxidation and other chemical reactions as it begins to dissolve on the surface. There is therefore a need for a means to quickly overcome surface tension;
Thus, a need has been recognized for a method of introducing light gauge scrap through the float and skim into the underlying melt.

Initially, attempts were made to mechanically force light gauge scrap beneath the molten metal surface. Attempts have also been made to compress light gauge scrap into large bundles and mechanically force the large bundles below the surface of the molten metal. Both of these methods have been unsuccessful due to excessive melting losses and low scrap metal melting and recovery rates. Following this initial attempt, an improved method was developed in which light gauge scrap was introduced below the surface of the molten metal in an isolated melting chamber type furnace.

An example of such an improved system is U.S. Pat.
No. 4286985. In this example, molten metal is directed from the heating chamber to an upper portion of the melting chamber by a pump, and the relatively hot molten metal is applied to the upper portion of the melt pool in the melting chamber and in the chamber. The scrap on the melt surface is subjected to a stirring action and circulated downward into the melt.

Other devices have been introduced including various pump impeller arrangements designed to introduce directly into the melting chamber substantially below the surface level of the molten metal pool. An example of such a device is U.S. Pat. No. 3,984,234.
No. 4128415 and No. 4322245. In all of these devices, the scrap metal floating on the surface of the molten metal is drawn into the center of the melt pool by a fluid vortex created by a submerged impeller of a pump in the melt pool. . The pump impeller of such a system also serves the additional purpose of circulating molten metal from the melting chamber into the heating chamber and from the heating chamber to the melting chamber.

These systems have had some success in allowing relatively large quantities of light gauge metal scrap to be immersed in the melt without being exposed to contaminants and oxidation as such material melts. has been proven. However, these systems are not perfect in practice due to the excessive vortices created when the impeller is driven at a speed sufficient to rapidly immerse substantially all of the light gauge scrap into the melt pool. I couldn't succeed. This excessive turbidity tends to draw surrounding atmospheric gases into the melt by suction. These gases easily combine with the molten metal, producing high amounts of impurities. This phenomenon is described in U.S. Patent No. 4,322,245, column 4, 42~
Detailed in 50 lines. Thus, a system is needed that positively drives all of the light gauge scrap into the molten metal without the inclusion of atmospheric gases and that provides good circulation of the molten metal from the heating chamber to the melting chamber.

The present invention is a system for remelting light gauge scrap metal. The system includes a remelting furnace separated into a heating chamber and a melting chamber. There is no burner means directed towards the surface of the molten metal in the melting chamber. The refractory partition between the heating chamber and the melting chamber is provided with entry and exit means to facilitate circulation of molten metal from the heating chamber to the melting chamber and then back from the melting chamber to the heating chamber. Circulation of the molten metal is effected by a molten metal pump arrangement arranged to direct the flow of molten metal from the heating chamber to the melting chamber. The melting chamber has a structure that acts to create a gravity flow of the molten metal surface into the melting chamber, e.g., to remove floating light gauge scrap above the surface of the molten metal from the portion of the molten metal pool below that surface (the molten metal surface). Also included is an auger means which serves to direct the flow down the central area of the metal pool. In parallel with the gravity flow, a mechanical force is applied that mechanically immerses the light gauge scrap metal into the central region of the molten metal pool.

These and other features of the invention are more fully disclosed and described in the following specification, accompanying drawings, and claims.

FIG. 1 illustrates an elevational view of an auger attached to a partially cut away drive shaft section.

FIG. 2 illustrates a plan view of the impeller seen from - in FIG. 1.

FIG. 3 illustrates an elevational cross-sectional view of the auger drum.

FIG. 4 illustrates an auger assembly including a cross-sectional view of the auger drum and a cut away partial view of the auger drive shaft.

FIG. 5 is a cut away elevational view of another embodiment of an auger assembly in which the drum and auger are a single unit in the auger.

FIG. 6 is a plan view of another embodiment of the auger assembly shown in FIG. 5.

FIG. 7 is a schematic cross-sectional elevation view of a system for melting light gauge metal scrap.

FIG. 8 is a schematic plan view of a system for melting light gauge metal scrap.

FIG. 9 is a schematic cross-sectional elevation view of an alternative arrangement of a system for melting light gauge metal scrap.

FIG. 10 is a schematic plan view of an alternative arrangement of a system for melting light gauge metal scrap.

Referring to FIG. 1, auger 11 is shown in partially cut-away form. The auger 11 has three blades 13 and a hub 15. The auger 11 is generally in the form of an axial turbine and is formed as a spiral flute comprising the spiral cross-section of each of three blades. The hub 15 is internally threaded 19 and includes a solid bore 17 that receives a snug outer thread of the drive shaft 23. When the drive shaft 23 is screwed into the hub 15 and assembled,
A hole 25 is made in the lateral direction of this combined body, and a pin 27 is inserted to prevent the auger 11 from detaching from the drive shaft 23 during operation.

Referring to FIG. 2, the outer end 29 of the vane 13 is made concentric with the hole 17 to allow the auger 11 to fit snugly into the cylinder. The leading edge 31 and the trailing edge 33 are made to lie in parallel planes perpendicular to the outer end 29 of the blade 13.

In the present invention, the auger 11 requires at least one blade, but preferably three blades. However, the leading edge 31 of each blade 13
Importantly, it extends circumferentially around the outer end 29 of the auger to the extent that it overlaps the trailing edge 33 of the next adjacent vane 13 as best shown in the figure. When a single blade 13 is used, the leading edge 31 of the blade
extends circumferentially around the outer end 29 of the same vane 13 to the extent that it overlaps the trailing edge of that vane 13.

Referring to FIG. 3, an auger drum having a generally central cylindrical cross section is illustrated. It is axially perforated as shown in the figure. Hole 37
are sized so that drum 35 can be placed on the auger as shown in FIG. The counterbore 39 has a small diameter dimension so that a lip 41 is formed. lip 41
is located on the leading edge 31 of the vane 13 as shown in FIG.

As shown in FIGS. 3 and 4, the upper end of the drum is machined to a radius 43. Drum 35 is attached to auger 11 by refractory cement. In addition, the drum 35 is connected to the outer end 29 of the auger 11.
A hole may be drilled laterally inside and a pin may be inserted. However, this is not shown in the drawings. As mentioned above, the combination of auger 11 and drive shafts 23 and 35 will be referred to hereinafter collectively as auger assembly 45.

5 and 6, another embodiment of the auger assembly of the present invention is shown incorporating the auger 11' and drum 35' in one piece. In this alternative design, the hub 15' has a hole 37' extending axially therethrough. Referring to FIG. 6, hole 37' includes a keyway 47. Referring to FIG. In this alternative embodiment, the drive shaft (not shown) is not threaded into the hub 15', but rather has a corresponding keyway in the drive shaft (not shown) of FIGS. 5 and 6, respectively. It is secured in place by a matching key (not shown) in the keyway of the hub 15'. Furthermore, hub 1
5' wall and through the drive shaft 23' which fits snugly into the bore 37' of the hub 15'.
9' can also be used. In all other respects,
The auger assembly is as illustrated and described with reference to FIGS. 1-4.

7 and 8 are respectively an elevational view of the system of the invention in schematic form and a plan view of the system of the invention in schematic form. Remelting furnace 49 includes a heating chamber 51 and a melting chamber 53. A powerful drive assembly 55, for example an auger assembly 4 rotated by an electric motor.
5 is inserted into approximately the center of the melting chamber 53 and located near it. The wall separating heating chamber 51 from melting chamber 53 includes an inlet 59 and an outlet 61 . The molten metal pump 63 is disposed in the heating chamber 51, and as a result of its operation, molten metal flows into the melting chamber 53 through the inlet 59 and returns from the melting chamber 53 to the heating chamber 51 through the outlet 61, as a result of which FIG. The molten metal pump 63 is arranged for recirculation as best shown in FIG.

In FIG. 7, light gauge metal scrap 6
5 is shown positioned above the surface of the molten metal pool within the melting chamber 53. molten metal surface 65
is maintained at a vertical height above the lip 51 of the auger assembly 45 so that molten metal in the melting chamber 53 flows over the lip 41 of the drum 35 and downwardly through the holes 37 thereof. It's becoming like that. This flow pattern is shown schematically in FIG. 4, including the molten metal surface and the direction of power flow at the surface of the molten metal.

During operation, auger assembly 45 rotates in the direction indicated by arrow 67 in FIG. The nature of the operation of the auger assembly 45 is that the leading edge 31 first comes into contact with any unit of molten metal and light gauge scrap that the auger assembly 45 encounters. Rotation of the auger assembly causes downward spiral movement of molten metal below the surface of the melt. The molten metal present in the region of the melting chamber 53 and the drum 35 is
generally flows downwardly from auger 11 and pump 63
contact with the molten metal stream moving through the melting chamber 53 on the flow generated by the melting chamber 53. The flow of molten metal caused by the rotation of auger 11 and auger assembly 45 reduces the level of molten metal within auger assembly 45 on auger 11, as confined by drum 35. That is, the melting chamber 5
Molten metal from the enclosed portion of drum 3 flows by gravity over lip 41 and into the confines of drum 35.

As the molten metal flows by gravity over the lip 41 of the auger assembly, the light gauge scrap metal floating on the surface of the metal flows by gravity with it, and it flows into the melting chamber 53.
Further and at the same time, the light metal scrap floating on the surface of the molten metal follows the flow path of the working fluid in the central region of the melt in the melting chamber 53 thanks to the arrangement of the vanes 13 of the auger 11. Within limits, it is physically immersed downward into the center of the molten metal melt. The light metal scrap is ultimately brought into contact with molten metal flowing through melting chamber 53 by pump 63. Auger assembly 4
It is only necessary that the downward spiral flow produced by the rotation of drum 5 be sufficiently intense to cause a drop in the surface level of the molten metal within the confines of drum 35. The auger assembly 45 is located relatively close to the molten metal surface 65 and the lip 41 is closed to an extent sufficient to create a downward spiral induced gravity flow created by the rotation of the auger 45. located below the surface. Within the scope of the invention, the lip 4 on the molten metal surface 65 is
The height of 1 can vary with respect to the number of revolutions per minute at which the auger assembly 45 rotates. The auger assembly 45 is preferably not allowed to rotate at a speed approaching that at which a substantial amount of atmospheric gas is entrained in the downward spiral flow of metal.

Another system for melting light gauge metal scrap is shown in FIGS. 9 and 10. In other embodiments, an auger 11 is used. However, a slightly different design of the auger drum 69 is used in that the auger drum 69 has a hollow cylindrical cross-section with only a straight internal bore 71 and no stepped bore similar to the counterbore 39. do. This internal hole 71 is slightly larger in size than the outer end 29 of the vane 13. The auger drum 69 is installed stationary within the melting chamber, and is fixed to the wall by a mounting spacer 73 as shown in FIG. This mounting spacer 73 should comprise a refractory or other material with similar heat resistance as the wall 57. Auger drum 69 may be made from materials similar to those used for auger drum 35, but with other chemical and mechanical properties known to those skilled in the art for use in high temperature metal melting furnaces. It may be constructed of acceptable refractory or ceramic materials.

During operation, auger drum 69 remains stationary as auger 11 rotates. In all other respects, the operation of this light gauge scrap metal melting system is as previously described.

In accordance with the provisions of the patent statutes, there has been illustrated and described what is believed to represent the best embodiment of the invention, its preferred construction, and its best method of operation.
However, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

[Brief explanation of drawings]

FIG. 1 illustrates an elevational view of an auger attached to a partially cut away drive shaft section;
Figure 2 illustrates a plan view of the auger seen from - in Figure 1; Figure 3 illustrates an elevational sectional view of the auger drum; Figure 4 illustrates a cross-sectional view of the auger drum and a cutaway of the auger drive shaft. FIG. 5 is a cut-away elevational view of another embodiment of an auger assembly in which the drum and auger are one unit in the auger; FIG. 6 is a plan view of another embodiment of the auger assembly shown in FIG. 5; FIG. 7 is a schematic cross-sectional elevation view of a system for melting light gauge metal scrap; FIG. 9 is a schematic plan view of a system for melting light gauge metal scrap; FIG. 9 is a cross-sectional elevational schematic view of an alternative arrangement of the system for melting light gauge metal scrap; and FIG. 3 is a schematic plan view of another arrangement of the system for melting scrap; FIG.

Claims (1)

Claims: 1 a. Remelting furnace means divided into at least one heating chamber and at least one melting chamber; b. Remelting furnace means associated with and operating on each of the at least one heating chamber; c. heating means separate from each of the at least one melting chamber; c. each of the at least one heating chamber and the at least one heating chamber;
an inlet/outlet means located for causing the flow of molten metal between at least one of the two melting chambers and below the surface level of the molten metal within the remelting furnace means; d. and from each of the at least one heating chamber to at least one of the at least one melting chamber and from each of the at least one melting chamber to at least one of the at least one heating chamber. molten metal pumping means arranged to move said molten metal flow through said inlet/outlet means; and e separate from said molten metal pumping means and located within each of said at least one melting chamber; disposed below and near the surface level of the molten metal to cause a downward gravity flow of the surface level of the molten metal, and light gauge scrap metal located adjacent to the surface level of the molten metal; auger means operable to mechanically direct the molten metal downwardly and below the surface level of the molten metal substantially co-current with the gravity flow at the surface level of the molten metal. Equipment for remelting scrap metal. 2. Apparatus according to claim 1, wherein each of the at least one heating chamber and at least one of the at least one melting chamber are separated by insulating wall means. 3. Claim 3, wherein said refractory wall means comprises at least one refractory wall positioned to isolate each of said at least one heating chamber from at least one of said at least one melting chamber. The device according to item 3. 4. Claim 2, wherein said inlet/outlet means comprises at least one passage communicating between said at least one heating chamber and at least one of said at least one melting chamber through said heat-resistant wall means. Or the device according to item 2. 5. Apparatus according to claim 1, in which the remelting furnace means is isolated into one heating chamber and one melting chamber, and this isolation is effected by heat-resistant wall means. 6. The apparatus of claim 5, wherein said inlet/outlet means includes at least one passageway communicating between said one heating chamber and said one melting chamber. 7. said at least one passageway being located opposite and spaced apart from one another, and molten metal passing from said heating chamber to said melting chamber in a substantially straight path through one of said ports; Claim 6 comprising a pair of inlets and outlets arranged to flow from the melting chamber to the heating chamber through two of the inlets and outlets.
Apparatus described in section. 8. The apparatus of claim 1, wherein said auger means comprises an auger in the form of an axial turbine containing at least one helical groove. 9. the auger comprises: a an auger of an axial flow turbine having at least one helical groove; b an auger drum of hollow cylindrical cross-section axially surrounding the auger and to which the auger is mounted; and c. Claims 1, 2, 3, 4, comprising an auger and means for rotating the auger drum.
Apparatus according to item 5, 6, 7 or 8. 10 said auger is: a an axial turbine auger having at least one helical groove; b axially surrounding but isolated from said auger and mounted stationary within said at least one melting chamber; an auger drum having a hollow cylindrical cross-section; and c. means for rotating the auger within the drum.
Apparatus according to item 5, 6, 7 or 8. 11. The apparatus of claim 9 or 10, wherein the auger of the axial turbine has three spiral grooves.